This project has estabished a population~based registry of children with cerebral palsy (CP) in four San Francisco Bay Area counties. Elements completed or in progress include a) Study of demographic and medical characteristics related to the occurrence of cerebral palsy. A higher percentage of children with CP now than formerly were low in weight at birth, consistent with the increased survival of infants of low and very low birthweight. Older mothers, especially those of high parity, and mothers or fathers aged under 20 years, were at greater risk of producing a child with CP. The risk of CP was not related to when in pregnancy prenatal care began, nor to level of technology of the hospital of birth. b) Cerebral palsy in twins. Twin pregnancies produced a child with CP twelve times more often than singleton pregnancies. Much, but probably not all, of this risk was related to the tendency of twins to be low in birthweight. Twins of unlike~sex pairs, necessarily dizygotic, were not at lower risk than twins of like sex pairs. If one twin died in utero, the surviving co~twin was more than 100 times more likely than a singleton to have cerebral palsy. Twinning is increasing in developing countries, and is likely to contribute more children with CP. Paper submitted, a confirmation completed in another population, and results submitted for publication. c) Very low birthweight and risk for cerebral palsy. This study is examining infants born weighing under 1500 g, cases and controls, for factors that may contribute to risk of CP in very low birthweight children. A poster on this work has been accepted for the annual meeting of the Child Neurology Society in the fall, 1993. d) Dental markers. Among children with cerebral palsy whose anterior primary teeth could be examined, a third had developmental defects of enamel. These enamel hypoplasias were more often associated with low birthweight and prematurity, but even among infants with CP who were not premature or low in birthweight were associated with need for intensive care in the newborn period. Analyses are now underway comparing infants with CP and birthweight 2500 g or more whose teeth showed enamel hypoplasias dating to a month or more before birth, with children with CP or similar birthweight but normal teeth, and comparing these with normal controls of the same birthweight group, to evaluate the possibility that enamel defects may be clues to prenatal events that contribute to cerebral palsy. One paper on this work published, another is in preparation.